Vertical moulding of concrete

ABSTRACT

A method of moulding long concrete articles in a vertical mould which incorporates a mould liner ( 17 ) with drainage tubes ( 5 ) used to dewater the concrete when the mould is filled. The improvement is to close off the drainage tubes ( 5 ) during the filling of the mould to inhibit water loss in the concrete during filling. The drainage tubes ( 5 ) may incorporate one way valves or include inner tubes ( 15 ) that may be pressurized to inhibit water entering the drainage tube ( 5 ).

This invention relates to improvements in the moulding of concretearticles such as poles, piles or pipes in a vertical mould.

BACKGROUND TO THE INVENTION

The moulding of concrete pipes, hollow poles or piles in a verticalmould has been proposed in U.S. Pat. No. 4,996,013. The mould is filledfrom the bottom and the concrete is compressed between an inner andouter mould by moving the inner mould outwardly using a flexiblemembrane. Water drained from the concrete into drainage galleries ortubes in the membrane. Because water segregates from the concrete duringthe filling of the mould water tended to accumulate in the upper sectionof the mould during filling. This problem was addressed in U.S. Pat. No.6,284,172 by capping the end of the mould to allow egress of fluid butretain particulates and stopping the filling of the mould when thepresence of solid materials at the end cap is sensed.

Although these methods produce poles of adequate strength the surfacefinish of the articles is sometimes rough and cavities form in thesurface during stripping of the article from the mould. The dewateringstep also appears to proceed unevenly in the moulded product.

It is an object of this invention to overcome these problems and providea method and apparatus that produces poles, piles or pipes in a verticalmould with an acceptable surface finish.

BRIEF DESCRIPTION OF THE INVENTION

To this end the present invention provides a method of forming concretearticles in a vertical mould in which the concrete mix is pumped intothe mould from the bottom of the mould and the segregation of the wateris inhibited to maintain an homogenous viscosity as the concrete mixrises in the mould.

This invention is partly predicated on the discovery that surfacedefects and uneven dewatering are caused by segregation of the waterduring pumping of the concrete into the mould. This segregation allowslocalized regions to develop lower water to cement ratios than for thecomposition as a whole. It was discovered that segregation occursbecause water escapes through the drainage galleries or tubes in theflexible mould liners before the mould is completely filled.

Accordingly the present invention provides a method of moulding longconcrete articles in a vertical mould which incorporates a mould linerhaving drainage tubes used to dewater the concrete when the mould isfilled, the improvement being to close off the drainage tubes during thefilling of the mould to inhibit water loss in the concrete duringfilling.

More particularly the present invention provides a method of forminglong concrete articles in a vertical mould which includes the steps of

-   -   a) providing a mould liner having drainage tubes to allow water        to be removed from the wet concrete    -   b) providing reinforcing in the mould cavity    -   c) pumping wet concrete into the bottom of the mould under        pressure so that the concrete rises to the top of the mould    -   d) preventing water from leaving the drainage tubes during the        step of filling the mould with wet concrete    -   e) allowing water to drain from the drainage tubes after the        mould is filled.

This method is particularly suited for forming poles for use as powerpoles or street lighting or as piles for construction sites or even formaking concrete pipes.

In another aspect this invention provides a vertical mould for forminglong concrete articles having

-   -   f) an annular mould cavity defined by a core and an outer shell    -   g) a mould liner around the inner core of the mould cavity which        includes vertical drainage tubes incorporating vertically space        perforations to allow dewatering of the concrete    -   h) means associated with said drainage tubes to prevent water        leaving said drainage tubes during the filling of the mould        cavity

In another aspect the present invention provides a flexible mould linerincorporating drainage tubes to allow dewatering of the concrete whereinthe drainage tubes are at least partially closed during the filling ofthe mould to inhibit water loss and are opened when the mould is filledto allow water to escape.

The closing of the drainage tubes can be achieved in any suitable way.One way valves which prevent water from rising in the drainage tubes toa height not much greater than the level of concrete in the mould can beused. It has been found that one way valves situated at verticalspacings of between 50 and 250 mm are adequate but spacings of 100 mmare preferred.

Another alternative is to use a thin flexible inner tube in side thedrainage tubes which inner tube can be pressurized with air or fluid topress against the openings in the drainage tubes to prevent waterescaping from the concrete. When the inner tube is depressurized, watercan escape to allow dewatering of the concrete in the filled mould.

It is also possible to utilize water pressure from the mould filling topressurize the inner tube in the drainage tube. This can be done byclosing off the upper end of the inner tube or having a one way valve atthat end and having a drainage cock at the lower end. This means aslightly greater pressure is need to lift the concrete and some waterloss occurs but the homogenous viscosity of the concrete is maintained.

DETAILED DESCRIPTION OF THE INVENTION

Preferred embodiment of the invention is described with reference to thedrawings in which:

FIGS. 1 (plan view) and 2 (cross section) is a schematic illustration ofthe mould and mould liners utilizing the drainage tubes of thisinvention;

FIGS. 3A (cross section) and 3B (plan view) is a schematic illustrationof a first embodiment of the drainage tube of this invention;

FIGS. 4A (cross section) and 4B (plan view) is a schematic illustrationof a second embodiment of the drainage tube of this invention;

FIGS. 5A (cross section) and 5B (plan view) is a schematic illustrationof a third embodiment of the drainage tube of this invention;

FIGS. 6 (cross section) and 7 (plan view) illustrate a test rig used todetermine the effectiveness of the water control method of thisinvention.

The vertical mould for forming concrete poles is of the kind describedin U.S. Pat. No. 6,284,172 the contents of which are incorporated hereinby reference. The difference is that the drainage tubes in the filtermedia of the mould liner are modified in accordance with this invention.The mould is usually 12.5 metres high and concrete in a water/cementration of about 0.45 is pumped into the bottom of the mould. Once theconcrete comes into contact with the filter media water begins to bleedinto the drainage holes which are usually spaced at 50 mm centres. Thepressure required to raise the concrete 12.5 metres is approximately 830kPa but varies with the water to cement ratio, the aggregate used andthe complexity of the reinforcing in the mould cavity; whereas thepressure of a 12.5 metre head of water is approximately 138 kPa with theresult that the water is forced into the drainage tubes. The water lossis usually not homogenous and some portions of the concrete lose morewater than others.

To control and inhibit this water loss the drainage tubes of thisinvention are used. As shown in FIGS. 1 and 2 the mould cavity 2 isdefined by the inner core 16 and outer mould liner 17 and includes areinforcing cage of steel 3 around which the concrete is pumped. As theconcrete enters the mould 2 the water passes through the filter 4 andthen into the drainage tube 5 via the drainage holes 6. The drainagecock 7 is closed so that the water rises up the tube 5.

In FIGS. 3A and B a first embodiment uses nylon drainage tubes 5incorporated into the filter media 4 which have drainage holes 6 at 50mm centres. Inside the drainage tube 5 is a silicon tube 15 which isable to be filled with water or air under pressure to seal against theholes 6 in the tube 5. The fluid is introduced into the inner tube 15via the inlet 16 and the remote end 17 is sealed or tied.

An alternative arrangement is shown in FIG. 2 where the drainage tube 5includes non return valves spaced vertically 100 mm apart. The nonreturn valves may consist of a valve seat comprising an annular brassvalve seat 10 glued to the internal wall of the drainage tube 5 and afloating ball 9 adapted to seal against the valve seat and supported ona helical support 11 which in turn is supported on the upper face of thevalve seat located 100 mm below.

As concrete rises in the mould water enters the drainage tube andbecause the drainage cock 7 [FIG. 4] is closed the water risesvertically in the drainage tube 5. Initially water will rise to drainhole 8 and some will escape into the mould space until the concretereaches the level of hole 8. the water rising in the drainage tube 5will press the ball 9 against valve seat 10 and prevent further waterentering the drainage tube 5 until the concrete level rises to the levelof the drainage hole immediately above the valve seat 10. In this waythe water loss from the concrete is limited to the volume of thedrainage tubes in the 100 mm rise of the mould between valve seats. Whenthe mould is filled the drainage cock 7 is opened and the dewateringprocedure as outlined in U.S. Pat. No. 6,284,172 is followed.

A further embodiment is illustrated in FIGS. 5A and B. Inside thedrainage tube 5 is an inner tube 12 which has a non return, floatingball valve 13 at its upper end adjacent the top of the mould cavity. Aswater rises in the tube 12 it pushes out the air and when the waterreaches the non return valve the valve is closed and the pressure insidetube 12 increases. The water level in the tube 12 is always higher thanthe concrete level in the mould cavity and the higher pressure in thetube 12 presses the tube 12 against the drainage tube and prevents waterentering the tube 5 through the drain holes 14. When the mould cavity 2is filled the drain cock 7 is opened and the water in tube 12 flows out.When the dewatering procedure commences the pressure of the water in themould is greater than the pressure within the empty drain tube 12 sothat it collapses and allows water to enter tube 5 through the holes 14and drain away.

A test facility illustrating the effectiveness of one embodiment of thisinvention is shown in FIGS. 6 and 7. The test method was devised togenerate similar pump pressures and conditions to those experienced infilling a vertical mould about 12 metres high. Because of therestrictions caused by the presence of the reinforcing cage in the mouldspace the pressure rises to about 830 Kpa.

Tha apparatus was set up using a 12 metre long plastic PVC pipe 21 tosimulate a mould cavity. The reinforcing cage 22 consisting of a seriesof rings 23 fixed to a vertical rod 24 was inserted into the pipe 21 andheld in position by the ring 25. The drainage tube 28 consists of anylon tube extending the full height of pipe 21 and is arranged withinthe rings 23 of the cage 22. The drainage tube 28 is approximately 6 mmin internal diameter with 1 mm holes 29 at 50 mm spacings along its fulllength. A valve 27 is fitted at the lower end of tube 28. A filter media30 is wrapped around the tube 28 to prevent cement particles fromentering the drainage tube 28 through holes 29. Fitted neatly within thedrainage tube 28 is a silicon rubber tube 31 of external diameter ofabout 6 mm and internal diameter 4 mm. the tube 31 extends from the topof drainage tube 28 and finishes about 500 mm above the bottom of thepipe 21. At the upper end of the drainage tube 28 and inner tube 31 is aone way valve 32. A water trap 33 is arranged at the top of the pipe 21with an out let 34.

After initially spraying water down the pipe 21 concrete is pumped in atthe lower end of pipe 21. Immediately the concrete reaches the filtermedia 30 about the drainage tube 28 the pressure exerted by pumpingcauses water to pass through the holes 29 into the lower end of thesilicon tube 31. The water level in the drainage tube 28 rises morequickly in than the level of the concrete in the pipe 21 due to itslower specific gravity. At 117 Kpa which is the pressure equivalent tothe head of water in the 12 metre high tube 28 the water reaches the oneway valve 32 and closes it. The water pressure within the silicon tube31 closes the holes 29 in the drainage tube 28 so that no more water canbe separated from the concrete. The concrete rises to the top of pipe 21without showing signs of any segregation because the water loss is equalto the internal volume of the silicon tube 31 about 150 cc.

Following this test the concrete was withdrawn from pipe 21 and returnedto the pump. The tube 31 was then removed from the drainage tube 28. thepipe 21 and drainage tube 28 were flushed clean with water. The sameconcrete was pumped into the pipe 21. This time the water passingthrough the filter 30 and holes 29 rises up the drainage tube to thenext spaced hole 29 and flows back onto the top of the concrete column.This water is unable to remix with the concrete and remains segregated.As the concrete approaches the top of pipe 21 the water on top of theconcrete column overflows into the water trap 33 and is collected fromoutlet 34. The quantity of water lost was measured at 5000 cc. This testdemonstrates that the control of water entering the drainage tube duringthe filling of the mould maintains the homogeneity of the concrete andprevents water segregation with its consequential problems of unevendewatering and cracked product when cured.

Those skilled in the art of moulding concrete articles will realize thatthe present invention can be put into effect by a variety of means toinhibit water escaping the mould cavity during the filling of the mouldcavity as well as the methods and arrangements disclosed herein.

1. A method of forming concrete articles in a vertical mould in whichthe concrete mix is pumped into the mould from the bottom of the mouldand the segregation of the water is inhibited to maintain an homogenousviscosity as the concrete mix rises in the mould.
 2. A method of forminglong concrete articles in a vertical mould which includes the steps ofa) providing a mould liner having drainage tubes to allow water to beremoved from the wet concrete b) providing reinforcing in the mouldcavity c) pumping wet concrete into the bottom of the mould underpressure so that the concrete rises to the top of the mould d)preventing water from leaving the drainage tubes during the step offilling the mould with wet concrete e) allowing water to drain from thedrainage tubes after the mould is filled.
 3. A vertical mould forforming long concrete articles having a) an annular mould cavity definedby a core and an outer shell b) a mould liner around the inner core ofthe mould cavity which includes vertical drainage tubes incorporatingvertically space perforations to allow dewatering of the concrete c)means associated with said drainage tubes to prevent water leaving saiddrainage tubes during the filling of the mould cavity
 4. A mould asclaimed in claim 3 in which the drainage tubes incorporate an inner tubethat is able to be pressurized to close off the perforations in thewalls of the drainage tube.
 5. A mould liner as claimed in claim 3 inwhich the drainage tubes incorporate one way valves vertically spacedapart in the drainage tube.
 6. A flexible mould liner for use in themould of claim 3 which incorporates drainage tubes to allow dewateringof the concrete wherein the drainage tubes are capable of at leastpartially being closed during the filling of the mould to inhibit waterloss and are opened when the mould is filled.
 7. A mould liner asclaimed in claim 6 in which the drainage tubes incorporate an inner tubethat is able to be pressurized to close off the drainage holes in thewalls of the drainage tube.
 8. A mould liner as claimed in claim 6 inwhich the drainage tubes incorporate one way valves vertically spacedapart in the drainage tube.
 9. Long concrete articles formed by theprocess of claim 1 or 2.